This invention is in the field of reflective films. This invention relates generally to an improved solar reflector for reflecting a majority of incident solar radiation, for example, for applications of concentrating solar power.
The overall reflectivity of solar reflectors is primarily dependent upon the reflection efficiency of the active reflective materials in the solar reflector as a function of the wavelength of incident solar electromagnetic radiation. Early thin-film reflectors incorporated thin aluminum films as the active reflector. For example, U.S. Pat. No. 4,307,150 for Weatherable Solar Reflector, issued on Dec. 21, 1981, discloses a solar reflector comprising an aluminum surface deposited over a flexible polyester support sheet. Later, silver thin-film reflectors were utilized, since silver is higher in reflectance than aluminum for most wavelengths of the solar spectrum. U.S. Pat. No. 4,645,714 for Corrosion-resistant Silver Mirror, issued on Feb. 24, 1987, discloses a specular reflective mirror film comprising a silver surface deposited over a polyester support film.
More recently, advanced optical materials and structures were incorporated into solar reflectors. For example, U.S. Patent Application Publication US 2012/0011850 for Broadband Reflectors, Concentrated Solar Power Systems, and Methods of Using the Same, published on Jan. 19, 2012, discloses a broadband UV-reflective multilayer optical film including alternating layers of higher and lower refractive index materials in a quarter-wave stack configuration, optimized for reflecting incident UV radiation.